Fulminic acid: a quasibent spectacle,Physical Chemistry Chemical Physics

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Fulminic acid: a quasibent spectacle
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2024-08-28 , DOI: 10.1039/d4cp02700k
Ashley M Allen ₁ , Laura N Olive ₁ , Patricia A Gonzalez Franco ₁ , Shiblee R Barua ₁ , Wesley D Allen ₁ , Henry F Schaefer ₁

Affiliation

Fulminic acid (HCNO) played a critical role in the early development of organic chemistry, and chemists have sought to discern the structure and characteristics of this molecule and its isomers for over 200 years. The mercurial nature of the extremely flat H–C–N bending potential of fulminic acid, with a nearly vanishing harmonic vibrational frequency at linearity, remains enigmatic and refractory to electronic structure theory, as dramatic variation with both orbital basis set and electron correlation method is witnessed. To solve this problem using rigorous electronic wavefunction methods, we have employed focal point analyses (FPA) to ascertain the ab initio limit of optimized linear and bent geometries, corresponding vibrational frequencies, and the HCN + O(³P) → HCNO reaction energy. Electron correlation treatments as extensive as CCSDT(Q), CCSDTQ(P), and even CCSDTQP(H) were employed, and complete basis set (CBS) extrapolations were performed using the cc-pCVXZ (X = 4–6) basis sets. Core electron correlation, scalar relativistic effects (MVD1), and diagonal Born–Oppenheimer corrections (DBOC) were all included and found to contribute significantly in determining whether vibrationless HCNO is linear or bent. At the all-electron (AE) CCSD(T)/CBS level, HCNO is a linear molecule with ω₅(H–C–N bend) = 120 cm⁻¹. However, composite AE-CCSDT(Q)/CBS computations give an imaginary frequency (51i cm⁻¹) at the linear optimized geometry, leading to an equilibrium structure with an H–C–N angle of 173.9°. Finally, at the AE-CCSDTQ(P)/CBS level, HCNO is once again linear with ω₅ = 45 cm⁻¹, and inclusion of both MVD1 and DBOC effects yields ω₅ = 32 cm⁻¹. A host of other topics has also been investigated for fulminic acid, including the dependence of r_e and ω_i predictions on a variety of CBS extrapolation formulas, the question of multireference character, the N–O bond energy and enthalpy of formation, and issues that give rise to the quasibent appellation.

中文翻译：

雷米酸：准奇观

雷米酸 (HCNO) 在有机化学的早期发展中发挥了关键作用，200 多年来，化学家一直在寻求辨别该分子及其异构体的结构和特征。雷酸的极其平坦的 H-C-N 弯曲势的多变性质，在线性时具有几乎消失的简谐振动频率，对于电子结构理论来说仍然是神秘且难解的，因为轨道基组和电子相关方法的巨大变化是见证了。为了使用严格的电子波函数方法解决这个问题，我们采用焦点分析 (FPA) 来确定优化的线性和弯曲几何形状的从头算极限、相应的振动频率以及 HCN + O( ³ P ) → HCNO 反应能。采用了 CCSDT(Q)、CCSDTQ(P) 甚至 CCSDTQP(H) 等广泛的电子相关处理，并使用 cc-pCV X Z ( X = 4–6) 基础进行完整基组 (CBS) 外推套。核心电子关联、标量相对论效应 (MVD1) 和对角玻恩-奥本海默校正 (DBOC) 都包含在内，并且被发现对确定无振动 HCNO 是线性还是弯曲有显着贡献。在全电子（AE）CCSD（T）/CBS水平上，HCNO是具有ω ₅ （H–C–N弯曲）= 120 cm ^-1的线性分子。然而，复合AE-CCSDT(Q)/CBS计算给出了线性优化几何结构下的虚频率(51 i cm ^-1 )，导致H-C-N角为173.9°的平衡结构。最后，在AE-CCSDTQ(P)/CBS水平上，HCNO再次与ω ₅ = 45 cm ^-1呈线性，并且包含MVD1和DBOC效应产生ω ₅ = 32 cm ^-1 。关于雷酸，还研究了许多其他主题，包括re和_ω预测对各种 CBS 外推公式的依赖性、多参考特征问题、N-O 键能和生成焓，以及产生准称谓。

更新日期：2024-08-28

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